Java CompositeConfiguration usage

a.properties

# Properties definining the GUI
colors.background = #FFFFFF
colors.foreground = #000080

window.width = 500
window.height = 300
version = old

b.properties

# Properties definining the GUI

# this should show up
colors.new = #ABCDERF

# this will be overridden by in-memory config
version = bversion

# this will be overridden too
window.width = 1000

build.gradle

apply plugin: 'java'

dependencies {
    implementation "commons-configuration:commons-configuration:1.6"
}

repositories {
    mavenCentral()
}


task runFinalJar(type: JavaExec) {
    group = "Run"
    classpath = files('build/libs/conf-test.jar')
    classpath += sourceSets.main.runtimeClasspath
    main = 'test.PropMain'
 }

 runFinalJar.dependsOn('build')

PropMain.java

package test;

import org.apache.commons.configuration.CompositeConfiguration;
import org.apache.commons.configuration.Configuration;
import org.apache.commons.configuration.PropertiesConfiguration;
import org.apache.commons.configuration.BaseConfiguration;
import java.util.Iterator;


class PropMain {
    private static CompositeConfiguration globalConfig = new CompositeConfiguration();
    private static PropertiesConfiguration configa;

    public static void main(String[] args) throws Exception {
        readSaved();

        applyVersionIfNew();

        saveIfChanged();

        readb();

        printGlobal();

    }

    private static void applyVersionIfNew() {
        if (!globalConfig.getString("version").equals("3.3.4.2")) {
            System.out.printf("Changing GlobalConfig version to 3.3.4.2 from %s\n", globalConfig.getString("version"));
            globalConfig.setProperty("version", "3.3.4.2");
        }
    }

    private static void readSaved() throws Exception {
        configa = new PropertiesConfiguration("a.properties");
        globalConfig.addConfiguration(configa);
    }

    private static void readb() throws Exception {
        PropertiesConfiguration configb = new PropertiesConfiguration("b.properties");
        globalConfig.addConfiguration(configb);
    }


    private static void saveIfChanged() throws Exception {
		Configuration changes = globalConfig.getInMemoryConfiguration();
        Iterator<String> iter = changes.getKeys();
        
        if (iter.hasNext()) {
            System.out.printf("****Update a.properties\n");
            while (iter.hasNext()) {
                String key = iter.next();
                Object value = changes.getProperty(key);
                configa.setProperty(key, value);
            } 

            configa.save();
        }        
    }

    private static void printGlobal() {
        Iterator<String> keysg = globalConfig.getKeys();
        while(keysg.hasNext()) {
            String key = keysg.next();
            String prop = globalConfig.getString(key);
            System.out.printf("Key %s Value %s\n", key, prop);   
        }
    }
}